Castro,
25, posted a 4.01 ERA in 29 starts between the in the Blue Jays' Double-A and Triple-A organizations last season. He has also spent time in the Phillies, Rangers and White Sox organizations.

Gabbard, who was part of the Eric Gagne trade in 2007, signed a minor league deal with the Red Sox. He was re-acquired by the Red Sox from the Rangers last summer, but pitched poorly upon his return to the organization.